It is well known in the art of subterranean drilling to use a drilling fluid to remove cuttings and to cool the bit. It is further known to use nozzles that are mounted on the bit body to control and direct the drilling fluid. The drilling fluid is typically forced through the drill string under pressure, so as to exit the nozzles with some desired velocity. The drilling fluid can be any of a variety of materials, including but not limited to air, water, and drilling mud (oil- or water-based). Nozzles control the direction, flow rate, and back-pressure of the fluid and provide a medium to communicate the drilling fluid from the bit body to the drilling environment. FIG. 1 illustrates nozzle placement on a standard drill bit 1, with a nozzle boss 16 having a mini-extended nozzle 12 extending therefrom and held in place by a hex-head retainer 14. FIG. 2 shows a standard nozzle 22 installed in a nozzle cavity 25 in jet boss 16. The standard nozzle 22 is retained in nozzle cavity 25 with a threaded retainer 20. The nozzle cavity 25 is in fluid communication with internal cavities of the bit (not shown) that receive drilling fluid from the drill string. FIG. 3 shows a mini-extended nozzle 32 installed in nozzle cavity 25. The prior-art mini-extended nozzle is distinguished from the standard nozzle by the extended portion 26 of the nozzle that is reduced in diameter and extends beyond the furthest most surface of the boss 16. The major diameter of the prior-art mini-extended nozzle is of the same length as the total height of the standard nozzle to ensure interchangeability. Both the standard nozzle and the mini-extended nozzle are manufactured from an erosion resistant material such as tungsten carbide. The nozzle cavity can be manufactured in many different locations on the rock bit through the use of common prior-art attachments such as extended nozzle tubes or different machining locations.
Fluid nozzles have conventionally been made from erosion resistant materials such as, coated steels, cemented tungsten carbide, ceramic, composites, and many other materials. Nozzles used on bits in the petroleum industry have to be able to withstand much more rigorous downhole conditions than nozzles used in the mining industry. This is because petroleum drilling uses mud as the drilling fluid, as opposed to mining drilling, where air is the drilling fluid.
Common methods used to retain the fluid nozzles in the drill bit nozzle cavities include threaded retainers 20 as shown in FIG. 2 and disclosed in U.S. Pat. No. 4,687,067, deformable pins as disclosed in U.S. Pat. No. 4,427,221, and snap retainers 24 as shown in FIG. 5 and disclosed in U.S. Pat. No. 3,115,200. A nozzle retention mechanism or system is necessary because the nozzle sustains axial loads from the drilling fluid passing through the nozzle, which tend to force the nozzle out of the nozzle cavity. The nozzle retention mechanism also facilitates field installation of various sizes and types of nozzle configurations into the bit.
One problem with current methods of retaining the fluid nozzle is that the retention method can fail, resulting in the nozzle blowing out of the bit. In particular, if the nozzle were made from cemented tungsten carbide or similarly hard material, the cutting structure could suffer damage when the nozzle came in contact with the cutting structure while drilling. Also, the hydraulic energy loss resulting from the increase in nozzle exit area would markedly reduce drilling efficiency. Hence, it is desirable to minimize the risk of nozzle blow-out.
Retention methods occasionally fail as a result of the high level of bit vibration experienced during drilling. Nozzle blow-outs can also result from mechanical failure of the deformable pin, retaining ring, or threaded retainer, or from any of these elements backing out or coming loose while drilling.
Still referring to FIG. 2, standard drill bit nozzles 22 generally do not extend beyond the nozzle boss 16. The outer surface of the nozzle is typically cylindrical in shape. Likewise, the inside diameter of the retainer 20 is cylindrical. Retainer 20 includes an inner, annular shoulder 21 and a threaded outer surface 23. Shoulder 21 receives and engages nozzle 22 to prevent it from blowing out, while threads 23 engage corresponding threads in nozzle cavity 25 located in nozzle boss 16, to prevent axial movement of retainer 20.
Unlike standard nozzles, mini-extended nozzles 32 extend beyond the nozzle boss 16, as shown in FIG. 3 and are employed to obtain higher fluid energy levels at the hole bottom than would be realized with a standard nozzle. As shown in FIG. 3, mini-extended nozzles 32 are typically held in place by a threaded retainer 30 having a shoulder 36 and external threads 33 as discussed before. The higher fluid energy levels at the hole bottom that available with mini-extended nozzles 32 improve the hole bottom and bit cleaning during drilling, thus improving the bit's rate of penetration and bit performance.
One problem with the conventional mini-extended nozzles 32, as illustrated in FIG. 4, is that if the nozzle hits an obstruction, the impact may break the mini-extended nozzle. The problem is increased when the nozzle is constructed from a brittle material such as tungsten carbide. If the nozzle is broken, pressure losses and possible nozzle washout could result in a trip out of the hole to replace the damaged nozzle or the entire bit. Such trips are very costly and as great efforts are made to reduce the risks of such events. Furthermore, the carbide from a broken tungsten carbide nozzle can damage the cutting structure, noticeably reducing the bit's usable life. One previous solution to this problem was to place a shrouded retainer around the extended portion of the nozzle as shown in FIG. 2 of U.S. Pat. No. 5,494,122. The shrouded retainer of the '222 patent includes threads for engaging the nozzle cavity and an annular lip for receiving the nozzle, and further includes a shroud or extension that is concentric with the nozzle and extends beyond the tip of nozzle boss 16. The '222 patent teaches that an annular gap should be left between the outside wall of the nozzle and the inside wall of the shroud, so as to allow the shroud to absorb the shock of contact with an object without damage to the nozzle. Thus, while the shroud does help protect the nozzle from impact, it has been found that fracture can still occur because the nozzle extension is not in contact with the shroud and thus is radially unsupported from the nozzle's axial shoulder to its exit port. This is particularly the case in instances where an object downhole impacts the portion of the nozzle that extends beyond the shroud.
Referring now to FIG. 5, nozzles generally employ at least one elastomeric sealing member 8 to seal around the nozzle where it is secured into the bit. The purpose of the elastomeric seal is to ensure that the drilling fluid is directed through the nozzle rather than around the outside of the nozzle, which would lead to an undesirable washout. Typically, nozzle seals 8 are radial static seals that fit into either a fully encapsulated seal gland 9 as shown in FIG. 5, or, more preferably, into a semi-encapsulated seal gland 10 as shown in FIG. 2. Part of the top of the semi-encapsulated seal gland 10 is defined by the bottom of the threaded retainer. The advantage of the semi-encapsulated seal gland 10 is that it is easier to remove or install the seal. Other seal gland variations exist, for example U.S. Pat. No. 4,400,024 uses a crushed O-ring gland configuration. It will be understood that the concepts of the present invention can be applied to nozzles that are sealed with any suitable sealing device.